Aluminum supports for planographic printing plates

ABSTRACT

This invention relates to a method for improving the receptivity for adhesively applied coatings of an aluminum surface which comprises treating the surface with a solution comprising at least one trihydroxybenzene carboxylic acid and drying. The invention also includes a reproduction material using the treated aluminum and a process for making a printing plate from the said reproduction material.

United States Patent Inventor Fritz Uhlig Wiesbaden-Biebrich, Germany Appl. No. 583,993 Filed Oct. 3, 1966 Patented Jan. 11, 1972 Assignee Kalle Aktiengesellschait Wiesbaden-Biebrich, Germany Priority 061. 6, 1965 Germany K 57319 ALUMINUM SUPPORTS FOR PLANOGRAPHIC PRINTING PLATES 6 Claims, No Drawings Hartsuch, Chemistry of Lithography," 195 2, LTF Foundation,pp I31- 132 Primary ExaminerGeorge F Lesmes Assistant Examiner-R. E. Martin Atlorney-lames E. Bryan ABSTRACT: This invention relates to a method for improving the receptivity for adhesively applied coatings of an aluminum surface which comprises treating the surface with a solution comprising at least one trihydroxybenzene carboxylic acid and drying. The invention also includes a reproduction material using the treated aluminum and a process for making a printing plate from the said reproduction material.

ALUMllNUM SUPPORTS FOR PLANOGRAPHIC PRINTING PLATES Aluminum used as support material for the preparation of planographic printing plates must be pretreated to ensure good adhesion of the reproduction layer. Thus, bright aluminum already has been mechanically treated with graining devices such as steel or plastic brushes in order to obtain a suitable support material. However, on material pretreated in this manner, light-sensitive layers do not adhere to such a degree as is desirable for printing very long runs. Further, aluminum surfaces already have been precleaned with alkaline agents, then etched with nitric acid, if desired, and finally treated with aqueous solutions of alkali silicates. Aluminum pretreated in this manner has the disadvantage that only a few types of light-sensitive layers, all of them negative working, adhere thereto.

Also, aluminum used for reproduction purposes has been electrolytically pretreated. This process, however, is very expensive, in particular as regards the current supply when a continuous process is employed or aluminum webs of large width are treated.

Further, planographic printing plates are known which contain, between the aluminum support and the copying layer thereon, a thin layer consisting wholly or partially of polymeric acids and/or derivatives thereof. Because of unavoidable variations in their degree of polymerization, these polymeric acids tend, in some cases, to cause differences in the quality of the planographic printing plates prepared therewith.

The present invention provides an aluminum support for planographic printing plates which has on at least one surface thereof a thin layer of at least one trihydroxybenzene carboxylic acid, and, if desired, a reproduction coating on this thin layer.

Preferably, the easily obtained and inexpensive 3,4,5- trihydroxybenzene carboxylic acid-(1), also known as gallic acid, is used as the trihydroxybenzene carboxylic acid component. However, the less known isomeric compounds, i.e., 2,3,4-trihydroxybenzene carboxylic acid-(1), also known as pyrrogallol carboxylic acid, and 2,4,6-trihydroxybenzene carboxylic acid, also known as phloroglucinol carboxylic acid, and digallic acid, also are suitable for the purposes of the present invention.

For the preparation of the support material according to the present invention, commercial aluminum, generally in the form of plates or, if a continuous process is used, in the form of webs, is first provided on one or both surfaces with a layer containing at least one trihydroxybenzene carboxylic acid. Known methods for the application of coatings are used; for instance, if both sides of the aluminum are to be coated, it may be immersed in a cold or, preferably, hot solution of trihydroxybenzene carboxylic acid in water or another inorganic or organic solvent. If only one surface is to be coated, the trihydroxybenzene carboxylic acid solution may be applied to the rotating support material, e.g. by spraying.

In addition to the aqueous solutions of trihydroxybenzene carboxylic acids, their solutions in water-containing organic solvents, e.g. ketones, such as acetone; cyclic ethers, such as dioxane; alcohols, such as methanol, ethanol or isopropanol; and glycol ethers, such as ethyleneglycol monomethylether, or dimethyl formamide, are suitable.

Mixtures of such solvents also may be used.

Before coating it with trihydroxybenzene carboxylic acid, the aluminum, if desired, may be subjected to a known precleaning treatment, e.g. with hot alkali phosphate or alkali carbonate solutions, with oxidizing agents, with dilute nitric acid, or with nitrate, chromate, or hydrogen peroxide solutions. Alternatively, the aluminum may be precleaned cathodically or anodically by means of an electric current. However, these precleaning methods nonnally can be dispensed with.

Depending upon the nature of the aluminum foil, the temperature applied and the concentration of the acid, the time required for coating ranges from a few seconds to several minutes. Generally, a treatment time of 5 seconds to l0 minutes at temperatures ranging from 30 to l00 C. will suffice. The concentration of trihydroxybenzene carboxylic acid in the solutions applied during this treatment ranges from about 0.0l to about l0 percent by weight; 2- to 5-minute treatment times with 0.1 to l percent by weight solutions at temperatures between 60 and C. are preferred. Alternatively, the treatment may be prolonged, or solutions of higher or lower concentration used. However, operating outside the ranges given above often is less advantageous or causes no improvement of the results obtained. If the aluminum plates are to be treated by the immersion process, there may be used, e.g., a 1 percent solution in warm water or one of the aforementioned organic solvents. If the solution is applied to the rotating support material, 0.1 to 2 percent solutions of the acid in an organic solvent or a mixture of several organic solvents are preferred.

Substances which are suitable for improving the hydrophilic properties of the aluminum surface, in particular hydrophilic colloids, such as cellulose ethers, e.g. carboxymethyl cellulose, hydroxyethyl cellulose, or methyl cellulose, or alginates, may be added to the solutions of the trihydroxybenzene carboxylic acid.

By treating aluminum with trihydroxybenzene carboxylic acid in accordance with the present invention, excellent hydrophilic properties are imparted even to greasy, hydrophobic rolled aluminum.

The trihydroxybenzene carboxylic acid layer thus produced may be briefly rinsed with water and dried. By drying at an elevated temperature, up to about C., the adhesion of the layer is advantageously increased. The aluminum support thus coated with trihydroxybenzene carboxylic acid retains its hydrophilic properties over a long period and may be stored or shipped. In the latter case, sensitization of the support is effected at a later date, if desired immediately preceding printing. However, the desired reproduction layer may be applied to the aluminum support immediately after the trihydroxybenzene carboxylic acid layer has dried.

For sensitization, the aluminum support is coated in the customary manner, either manually or by means of suitable coating machines, with the reproduction coating consisting or organic substances, suitably in dissolved form, either by immersion, roller application, or application to the rotating material, and subsequent removal of the solvent. Aluminum supports covered with a uniform, homogeneous layer are obtained which can be converted by known methods into printing plates ready for printing.

Suitable reproduction layers for the planographic printing plates of the invention are, quite generally, such layers which can be imagewise differentiated by the influence of visible, ultraviolet, or infrared light, by X-rays or by heated bodies. The following light-sensitive organic compounds are exemplary: aliphatic and aromatic esters; hydrazides and amides of naphthoquinone diazide sulfonic acids; cinnamalmalonic acid and the substitution products and functional derivatives thereof; diazonium salts of substituted and unsubstituted amino diphenylamine and condensation products thereof with formaldehyde; 0- and p-quinone diazides of benzene, anthracene or heterocyclic systems, e.g. quinoline, indazole, benzimidazole, fluorene, or diphenylene oxide; diazo ketones; unsaturated ketones; oand p-iminoquinone diazides; derivatives of alkyl nitronaphthalene-sulfonic acids; nitroaldehydes; acenaphthenes; nitrones; stilbenes; azides and diazides; and relatively highly polymeric diazo compounds. Further, reproduction layers may be applied which possess a high elec trical resistance in the dark which, however, decreases by several powers of ten when the material is exposed to light or heat influence, such as are used in electrophotographic and electrothermographic processes, e.g. organic photoconductors of low and high molecular weight, if desired in admixture with resins. Oxadiazoles, imidazolones, triazoles, oxazoles, thiazoles, hydrazones, triazines, polyvinly carbazoles and polyvinyl oxazoles have proved to be particularly suitable photoconductors. Suitable resins are those which contain groups that render them alkali soluble, such as acid anhydride groups, carboxylic acid groups, sulfonic acid groups, sulfonamide groups or sulfonimide groups, e.g. vinyl polymers and vinyl copolymers, phthalic acid ester resins, maleinate resin, alkyd resins, colophony resins and polyacrylic acid resins.

The aluminum supports of the present invention have the advantage that practically all known types of reproduction coatings adhere well to the trihydroxybenzene carboxylic acid layer and, in addition, they yield, after the usual imagewise exposure and development, longer runs in the machines customarily used for offset printing than the hitherto used mechanically roughened aluminum foils. Moreover, the aluminum supports of the invention and the planographic printing plates prepared therefrom have the additional advantage that they can be very easily prepared because commercial rolled aluminum may be directly subjected to a trihydroxybenzene carboxylic acid treatment in a bath.

In the following examples, 1 part by volume is 1 ml. if the unit by weight is 1 g.

EXAMPLE 1 A mechanically roughened aluminum foil is immersed for 120 seconds in a 1 percent by weight solution of 3,4,5- trihydroxybenzene carboxylic acid in water at 80 C. After drying, the pretreated foil is coated with a 1 percent by weight aqueous solution of the zinc chloride double salt of a diazo compound prepared by condensing 1 mole of 4-diazo-diphenylamine and 1 mole of formaldehyde in sulfuric acid. After exposure of the foil under a master, the diazo compound is removed from the areas not struck by light by rinsing with water and the image areas are inked up with greasy ink. Printing then can be performed as usual.

The adhesion of this diazo compound to an aluminum foil which had been only mechanically roughened is poor.

EXAMPLE 2 An electrolytically roughened aluminum foil is immersed for minutes in a 1.5 percent by weight solution of 2,4,6- trihydroxybenzene carboxylic acid in water at 90 C. After drying with warm air, the thus coated aluminum foil is stored for several months. It does not lose any of its desirable properties during storage.

After storage for four months, the foil is sensitized by wiping it over with a l percent by weight aqueous solution of the phosphate of a condensation product prepared by condensing diphenylamine-4-diazonium chloride and formaldehyde in 85 percent by weight phosphoric acid. After exposure under a photographic negative, the entire foil is wiped over with a sponge soaked in water, whereby the layer is removed from the areas not struck by light. The light-hardened areas of the reproduction layer are covered with a lacquer according to the procedure of German Pat. No. 1,180,869, and then inked up with greasy ink, while the trihydroxybenzene carboxylic acid layer adhering to the nonimage areas of the aluminum repels greasy ink. Printing is then performed as usual.

EXAMPLE 3 A web of crude rolled aluminum is passed at 95 C. through a bath consisting of a solution of 0.5 percent by weight of 2,3,4-trihydroxybenzene carboxylic acid and 0.01 percent by weight of carboxymethyl cellulose in water. The web is then dried and coated in known manner with a 2 percent by weight solution of 1-(4'-methylbenzene-1'-sulfonyl)-imino)-2-(2",5 '-dimethyl-phenyl-aminosulfonyl)-benzoquinone-( 1 ,4)-diazide-(4) in ethyleneglycol monomethylether, dried, and cut into individual sheets.

For the preparation of a printing plate, the coated side of the foil is exposed under a transparent original and then treated with a cotton swab soaked with an about 3 percent by weight solution of trisodium phosphate. A yellow-colored image of the original remains in the areas struck by light. After rinsing with water, the printing foil is inked up with printing ink and then may be used for printing in a printing machine.

EXAMPLE 4 An aluminum foil is coated on a rotating disk with a 2 percent by weight solution of gallic acid in 88 percent by weight of ethyleneglycol monomethylether and 10 percent of water, dried, and then coated, by the same method, with a 0.4 percent by weight solution of 4-diazodiphenylaminc-boron tetrafluoride and dried. After exposure under a master and removal of the layer from the unexposed areas by rinsing with water, an image is obtained which is a negative of the master used. After inking with greasy ink, the plate may used for printing.

EXAMPLE 5 An aluminum foil which had been pretreated with gallic acid as described in example 1, is coated with a solution containing 1.5 percent by weight of 2,2'-bis-(naphthoquinonel,2)-diazide-( 2)-sulfonyloxy-(5 )-dinaphthyl-( 1,1 methane in ethyleneglycol monoethylether. After exposure under a transparent original, wiping over of the image side with an approximately 5 percent by weight trisodium phosphate solution, and inking with greasy ink, the plate may be used for printing in a printing apparatus, direct images corresponding to the master being obtained.

EXAMPLE 6 An aluminum foil is coated on a rotating disk with a solution of 2 percent by weight of phloroglucinol carboxylic acid in a solvent mixture made up of 90 percent by weight of ethyleneglycol monoethyl ether and 10 percent of water, dried, and then coated, by the same method, with a 1 percent by weight solution of the naphthoquinone-( l,2)-diazide-(2)-5 -sulfonic acid ester of phloroglucinol in ethyleneglycol monoethylether and dried with hot air.

After exposure under a diapositive, a positive image of the master is obtained when the layer is removed from the areas struck by light by wiping over with a cotton swab soaked in a 3 percent by weight trisodium phosphate solution. The plate is then rinsed with water and an about 1 percent by weight phosphoric acid and the image areas are then inked up with greasy ink.

EXAMPLE 7 An aluminum foil which had been coated with gallic acid as described in example 1, is coated with a solution of 1 part by weight of 2,5-(4'-diethylaminophenyl-( l ))-l,3,4-oxadiazole, 0.8 part by weight of a styrene copolymerizate containing carboxyl groups and having a specific gravity of L26 to 1.28 and a decomposition range of from 200 to 240 C., and 0.003 part by weight of Rhodamine B extra (Schultz Farbstofitabellen, 7th edition, volume 1, No. 864) in 30 parts by volume of ethyleneglycol monomethylether and then dried.

For the preparation of images on the electrophotographic reproduction material thus produced, the layer is charged by means of a corona discharge, then exposed for 1 second under a master to the light of a watt mercury vapor lamp, and the electrostatic image of the master thus produced is made visible by dusting over with a resin powder colored with carbon black and fixed by heating to C., a permanent electrophotographic copy being obtained. For the preparation of a printing plate, the electrophotographic copy is wiped over with a solution consisting of 30 parts by weight of methanol, 20 parts by weight of glycerin, and 35 parts by weight of ethyleneglycol. Then, the plate is briefly rinsed with water and treated with a dilute, approximately 0.5 to 5 percent by weight aqueous phosphoric acid solution. After the printing plate thus obtained has been inked up with greasy ink, it may be used in the customary manner for printing in an offset printing being obtained.

6 It will be obvious to those skilled in the art that many 3. A reproduction material according to claim I in which modifications may be made within the scope of the present inthe acid is 2,4,6-trihydroxybenzene carboxylic acid. vention without departing from the spirit thereof, and the in- 4. A reproduction material according to claim I in which vention includes all such modifications. the acid is 2,3,4-trihydroxybenzene carboxylic acid.

What is claimed is: 5 5. A reproduction material according to claim 1 in which 1. A light-sensitive reproduction material comprising an the reproduction layer Comprises a light-Sensitive diam aluminum base, a first layer comprising at least one trihydrox- P ybenzene carboxylic acid, and a second light-sensitive A l'epl'odPctlon matel'lal according 1 Whlch reproduction layer on the first layer. the reproduction layer comprises a photoconductive com- 2. A reproduction material according to claim I in which 10 Pound the acid is 3,4,5-trihydroxybenzene carboxylic acid. 

2. A reproduction material according to claim 1 in which the acid is 3,4,5-trihydroxybenzene carboxylic acid.
 3. A reproduction material according to claim 1 in which the acid is 2,4,6-trihydroxybenzene carboxylic acid.
 4. A reproduction material according to claim 1 in which the acid is 2,3,4-trihydroxybenzene carboxylic acid.
 5. A reproduction material according to claim 1 in which the reproduction layer comprises a light-sensitive diazo compound.
 6. A reproduction material according to claim 1 in which the reproduction layer comprises a photoconductive compound. 